I have a '68 firebird with pwr brakes, front disc - original configuration. The fluid in the master cylinder is displaced from the front reservoir to the rear, overfilling the rear over time. The disc calipers are new or rebuilt. The master cylinder is rebuilt(sleeved, etc) and the proportioning valve is new. The only part I haven't done anything with is the distribution valve. I had the master cylinder rebuilt as it was suggested to me that the issue was with either the master cylinder or the proportioning valve and the proportioning valve was new. I still have the same problem. Before I replace the distribution valve because "its the only thing left" I thought I would ask the experts - any ideas as to what is causing the fluid to be pumped from the front to the rear reservoir?
I would still think it is in the master cylinder. The prop valve should not displace fluid into the other side of the master. I know it would be a lot of work. but, you could take the MC off of the car and do a very extensive bench bleed on it to see if the fluid is changing sides. I did this with one of my MC to isolate the problem.
Does the brake pedal slowly go to the floor when braking? That's what usually happens when I have had MC leak between reservoirs.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
So far, the pedal is firm. The pedal firmed up nicely after bleeding the braks following the MC install. I'll have to check with the engine off and see if the pedal depresses to the floor. Robert, The extensive MC bleed you mention, would this include plugging the front and rear outlets, to see if the fluid transfers whe pushing the piston? One factor I hadn't mentioned - as I replaced every component in the brake system, I changed from the DOT 3 to silicone. brake fluid I have had great success using silicone in my '55 T-Bird and it has worked well in the Firebird - would the use of silicone brake fluid be a factor? Thanks
I was told that you CANNOT "change" to DOT 5 unless you are looking at a completely dry system. Either every single component AND line is completely new or replaced. If there were any residue of any of the old DOT 3 or 4 ANYWHERE, you were going to have trouble.
You mentioned above that you had not done "anything" with the distribution valve. And what about the brake lines themselves?
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
I am saying that adding DOT 5 to a system that might have had left over amounts of DOT 3/4 can lead to problems. From what I read, it appears that a gel forms.
New DOT 5.1 is apparently totally compatible with earlier 3 and 4 systems.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI